Method and apparatus for determining hydrogen concentration in liquid sodium utilizing an ion pump to ionize the hydrogen

ABSTRACT

A device for and method of measuring hydrogen concentration in liquid sodium to detect water leaks into the sodium. A thin-wall, tubular, annealed nickel probe in contact with liquid sodium is connected to an ion pump. A vacuum is created within said nickel probe by the ion pump, causing hydrogen atoms in the liquid sodium to diffuse through the wall of the probe and be drawn into the ion pump wherein the hydrogen atoms are ionized. The current generated within the ion pump by the ionization of hydrogen atoms is measured, this current being indicative of the hydrogen concentration in the liquid sodium.

United States Patent Vissers et a].

[4 1 Aug. 8, 1972 [72] Inventors: Donald R. Vissers, Naperville; John T.Holmes, Downers Grove; Paul A. Nelson, Wheaton; Louis G. Bartholme,Joliet, all of 111.

[73] Assignee: The United States of America as represented by the UnitedStates Atomic Energy Commission [22] Filed: Nov. 24, 1970 [21] Appl.No.: 92,466

[52] US. Cl. ..324/33, 73/19, 176/19 R [51] Int. Cl. ..G0ln 27/00, G0ln7/00, G2lc 7/00 [58] Field of Search ..324/33; 73/19, 23; 176/19 E,

176/19 J, 19 R; 204/195 P [56] References Cited UNITED STATES PATENTS3,498,900 3/1970 Banks ..324/33 3,565,769 2/1971 Holden ..204/1953,451,256 6/1969 Kolodney ..73/19 2,671,337 3/1954 Halsberg ..73/232,882,212 4/1959 Beard ..204/195 Primary Examiner-Robert .l. CorcoranAttorney-Roland A. Anderson [57] ABSTRACT A device for and method ofmeasuring hydrogen concentration in liquid sodium to detect water leaksinto the sodium. A thin-wall, tubular, annealed nickel probe in contactwith liquid sodium is connected to an ion pump. A vacuum is createdwithin said nickel probe by the ion pump, causing hydrogen atoms in theliquid sodium to diffuse through the wall of the probe and be drawn intothe ion pump wherein the hydrogen atoms are ionized. The currentgenerated within the ion pump by the ionization of hydrogen atoms ismeasured, this current being indicative of the hydrogen concentration inthe liquid sodium.

11 Claims, 2 Drawing Figures METHOD AND APPARATUS FOR DETERMININGHYDROGEN CONCENTRATION IN LIQUID SODIUM UTILIZING AN ION PUMP TO IONIZETHE HYDROGEN CONTRACTUAL ORIGIN OF THE INVENTION The invention describedherein was made in the course of, or under, a contract with the UNITEDSTATES ATOMIC ENERGY COMMISSION.

BACKGROUND OF THE INVENTION This invention relates to the measurement ofhydrogen in liquid sodium. More specifically, the invention relates tothe measurement of the hydrogen concentration in the liquid sodiumcoolant of a sodiumcooled nuclear reactor for the purpose of detectingwater leakage into the liquid sodium.

A major concern in the operation of liquid sodiumcooled nuclear reactorsis water leakage into the liquid sodium occurring in the steam generatormodule. The steam generator is simply a heat exchanger in which heat istransferred from the sodium coolant system to water. The violentsodium-water reaction resulting from such a water leak causes rapidcorrosion and erosion of metal tubes adjacent to the leak. Asufficiently large or long-lasting leak could result in the deformationand rupture of the steam generator shell itself, the shell encasing thehot liquid sodium as well as the heat exchange tubes through which waterflows. Hence, it is imperative that even the smaller water leaks be detected immediately if propagation of damage is to be avoided.

The present invention is based on the detection of the hydrogen producedby the sodium-water reaction. The device and method according to thepresent invention detects and measures the change in hydrogenconcentration in the liquid sodium caused by this production ofhydrogen. Such a device and method require sensitivity and rapidresponse to changes in hydrogen concentration, as well as reliability.It would be desirable to be able to detect water leaks as small as 1.0 X10" lb/sec, which is safely below the leak rate at which significanterosion and wastage of metal from tubes adjacent to the leak occur. Thereaction products of such leaks, primarily hydrogen and oxygen dissolvedin liquid sodium, would be mixed with the entire sodium stream flowingfrom the steam generator. Therefore, to detect 1.0 X 10" lb/sec of waterleakage in the largest of steam generators, it would be necessary tomeasure an increase in the hydrogen concentration of about 0.004 ppm. Ata normal level of hydrogen in liquid sodium of about 0.1 ppm, thisamounts to about a 4 percent increase in the hydrogen concentration.Such a detection system must also respond rapidly to an increase inhydrogen concentration to allow rapid shutdown of the steam generator,yet with a minimum risk of unnecessary shutdown.

Other methods or devices for measuring the hydrogen concentration inliquid sodium include the following: Removing a sodium sample from thesodium coolant followed by any number of various laboratory techniquesfor determining the hydrogen concentration of the sample; usingmechanical or oil diffusion pumps in conjunction with a nickel or othermetal membrane permeable to hydrogen, placing the membrane in contactwith he liquid sodium, and causing the hydrogen in the liquid sodium todiffuse across the membrane until an equilibrium is achieved, afterwhich the amount of hydrogen in equilibrium is determined by a pressuregage; using an oil diffusion pump in conjunction with a nickel membranein contact with the liquid sodium, causing the hydrogen in the liquidsodium to continually diffuse across the nickel membrane, and from thisdetermining the hydrogen concentration in the liquid sodium with a massspectrometer; and removing hydrogen from the liquid sodium by diffusionacross a nickel-coated palladium membrane with subsequent oxidation ofthe hydrogen by the palladium to form H O which is then quantitativelymeasured. Some of these devices or methods, however, do not meet all therequirements necessary for such a leak detector. Either they are notmeasuring the hydrogen concentration continuously, are not sufficientlysensitive so as to detect the presence of the smaller leaks, or do notdetermine the hydrogen concentration and respond to any changes thereinsufiiciently rapidly so as to detect water leakage prior to significantmetal wastage and damage propagation.

It is therefore an object of this invention to provide a device for andmethod of measuring the hydrogen concentration in liquid sodium.

It is a further object to provide a device for and method of measuringthe hydrogen concentration in liquid sodium continuously and without thenecessity of removing sodium samples from the liquid sodium.

It is also an object of this invention to provide a device for andmethod of measuring hydrogen concentration changes in the liquid sodiumcoolant of a sodium-cooled nuclear reactor in a manner which is rapid,reliable and sufficiently sensitive so as to detect hydrogenconcentration changes resulting from water leakage into the sodiumcoolant as small as 10' lb/sec.

Another object of this invention is to provide a device for and methodof detecting water leaks into the liquid sodium coolant system of aliquid sodium-cooled nuclear reactor as small as 1.0 X 10 lb/sec bydetecting the hydrogen produced from the reaction which occurs whenwater contacts the liquid sodium.

Further objects and advantages of the invention will be apparent fromthe following detailed description of the device and method.

SUMMARY OF THE INVENTION In practicing this invention for the measuringof the hydrogen concentration in liquid sodium, a thin-wall, tubular,annealed nickel probe whose outer surface is in contact with the liquidsodium is connected to an ion pump. A voltage, accurately controlled ata very precise and constant level, is applied to the electrodes of theion pump. The ion pump creates a vacuum within the nickel probe ofapproximately 10' to 10' Torr, thereby causing hydrogen atoms in theliquid sodium to difluse through the wall of the nickel probe and bedrawn into the ion pump wherein the hydrogen atoms are ionized. Thecurrent generated by the ionization of the hydrogen atoms is measured.Because this current is linearly related to the number of hydrogen atomsionized within the ion pump, it is indicative of the hydrogenconcentration in the liquid sodium and thereby will indicate water leaksinto the liquid sodium coolant of a liquid sodium-cooled nuclear reactorby measuring increases in the hydrogen concentration of the liquidsodium resulting from such water leaks.

BRIEF DESCRIPTION OF THE DRAWINGS The invention device is illustrated inthe drawings, of which:

FIG. 1 is a view showing the components of a device illustrating anapplication of the present invention.

FIG. 2 is an enlarged, partially sectional view of a nickel probe usedin the practicing of the present invention.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 there is shown a deviceillustrating the application of the present invention whereby nickelprobe 10, connected to an ion pump 12 by way of tubing 14, is insertedinto pipe 16 which contains hot flowing liquid sodium. As nickel probeis evacuated to a pressure of 10' to 10" Torr by ion pump 12, thepartial pressure of hydrogen in the liquid sodium causes hydrogen atomsto diffuse through the wall of probe 10, after which the hydrogen atomsare drawn into ion pump 12 wherein they are ionized.

In order to initiate operation of ion pump 12, a vacuum of approximately10 Torr must first be created within probe 10, tubing 14 and ion pump12. Any means to accomplish this may be used. In the preferredembodiment, vacuum port 18, comprising a high-purity copper pinch-offfitting 20, is located between probe 10 and ion pump 12. A standardsorption vacuum pump is attached to fitting and is used to obtain thedesired vacuum of 10' Torr. Once this vacuum has been obtained and ionpump 12 put into operation, the sorption pump is pinched off at fitting20 and removed, fitting 20 retaining an air-tight seal after the removalof the sorption pump.

Pump controller 22 converts the AC. input, 110 A.C. in the illustrateddevice, to a DC. output and applies this output voltage to theelectrodes of ion pump 12 in the amounts as specified below. The voltagewhich is applied to the ion pump electrodes must be controlledaccurately at a very precise and constant level to the extent that theion pump current generated when hydrogen atoms are ionized is constantto within 10.1 percent, i005 percent in the preferred embodiment, forany particular concentration of hydrogen in the liquid sodium. Thisaccurately controlled voltage at a precise and constant level iscritical. If this is not maintained within the limitations given above,fluctuations in the applied voltage will cause inconsistent ionizationof hydrogen atoms within ion pump 12, resulting in ion pump currentfluctuations which bear no connection to changes in the hydrogenconcentration of the liquid sodium. If this were to occur, the devicewould not be sufficiently sensitive. This critically precise voltagelevel used in conjunction with the stated ion pump vacuum range of 10'to 10' Torr is what gives this device its significant sensitivity. Anyvoltage-regulating means for obtaining this precise and constant voltagelevel may be used. In the preferred embodiment, voltage regulator 24 isused to achieve this purpose.

FIG. 2 shows the preferred structure for nickel probe 10, although theinvention is not limited to the use of such a structure. Probe 10 isconstructed from nickel because of the facts that hydrogen will diffusethrough a thin nickel membrane and that nickel is chemically inert inliquid sodium. Probe 10 is tubular in shape and l to 4 inches in length,the particular device illustrated being 1 inch in length. It has aninner diameter no greater than 0.5 inch, the preferred diameter beingnine thirty-seconds inch is sufficiently small to allow the hydrogen tobe rapidly drawn away from the inner surface of wall 26, therebypromoting rapid hydrogen diffusion. Circumferential nickel fins 28 arethree thirty-seconds inch in height and number 15 per inch of probelength. The hollow fins 28 give probe 10 mechanical strength whilecreating a large surface area of approximately 40 cm in a l-inch-longfor sufficient hydrogen diffusion. The surface area of probe 10 is moreimportant than its actual length, for the surface area must besufficiently great, 10 to cm so as to be able to detect the hydrogen inthe liquid sodium. Wall 26 can range from 0.008 to 0.020 inch inthickness, the preferred thickness being 0.01 inch.

A critical characteristic of probe 10 is that it must be annealed at 600to 900 C. for 10 to 60 hours, the preferred annealing being performed at800 C. for 25 to 30 hours. This was discovered to be necessary if auniform diffusion rate of hydrogen through wall 26 is to be maintainedover an extended period of time while probe 10 remains in contact withhot liquid sodium. Without such annealing, the hot liquid sodium woulditself slowly anneal probe 10 over a period of time, thereby graduallyand continually changing the hydrogen diffusion properties of probe 10.This would result in the illustrated device being insufficientlysensitive and unreliable.

Turning back to FIG. 1, ion pump 12 contains two electrodes consistingof titanium plates 0.125 inch in thickness. Tantalum may also be used asthe cathode material. A voltage of 2,700 to 5,000 volts D.C., 4,750volts DC. in the preferred embodiment, is applied to the electrodes. Avoltage of less than 2,700 volts D.C. would result in insufiicientionization of hydrogen atoms, while greater than 5,000 volts D.C. wouldcause ion pump 12 to overheat. As hydrogen atoms are drawn into ion pump12, they are ionized between the two electrodes, thereby creating acurrent.

The size of ion pump 12, meaning thereby the pumping rate of the ionpump, can vary in accordance with the surface area of probe 10. In theparticular device illustrated, ion pump 12 has a pumping rate of 11liters/second. The lower limitation to the size of ion pump 12 would be1 liter/second, for below this pumping rate the size of probe 10 wouldbe sufficiently small so as to prohibit sensitive and reliablemeasurements of the hydrogen concentration in the liquid sodium. Theupper limitation to the size of ion pump 12 would be 20 liters/second,for a pumping rate greater than this would require very large fittingsas well as a very large probe 10, which is undesirable, if the desiredvacuum of 10' to 10" Torr is to be obtained.

Table I shows the fluctuations in the ion pump current when the appliedvoltage level is not accurately controlled at a precise and constantlevel. Table II shows how the presence of voltage regulator 24, only oneof many possible voltage-regulating means, results in a precise andconstant voltage applied to the ion pump electrodes, causing a much moreconstant and consistent ion pump current.

TABLE I Hydrogen concentration in sodium 0. 1 ppm lon pump current(uamps) taken at one-second intervals Mean 16.95 Standard Deviation o-0.392

TABLE II Hydrogen concentration in sodium 0. 1 ppm lon pump current(namps) taken at one-second intervals Mean 18.03 Standard Deviation a0.0107

K JT= S 1 The pressure of hydrogen within probe 10 is directly relatedto the current generated within ion pump 12. Therefore, from the readingof current meter 30, the hydrogen concentration in the liquid sodium canbe calculated either mathematically or from prepared graphs. However, apreferred method is simply to initially calibrate current meter 30 interms of known concentrations of hydrogen in liquid sodium, therebyeliminating any need for calculation and allowing the hydrogenconcentration in the liquid sodium to be determined directly fromcurrent meter 30.

When water leakage into the liquid sodium coolant of a sodium-coolednuclear reactor occurs, the normal level of hydrogen concentration inthe liquid sodium coolant changes. The basis for this change is thesodium-water reaction which occurs upon contact of the water with thesodium. The following formulas indicate this reaction:

4 Na H O 2 NaH N2 thereby causing an increase in the hydrogenconcentration level in the liquid sodium. Therefore, if the hydrogenconcentration of the liquid sodium coolant is measured continuously, anunexpected increase in this concentration at any time would indicate awater leak.

Measuring the hydrogen concentration in liquid sodium and changestherein was performed by connecting a thin-wall, tubular nickel probe,having been annealed at approximately 800 C. for 25 to 30 hours, to anion pump. The nickel probe and ion pump were then evacuated to 10' Torrusing a standard sorption vacuum pump. A voltage of 4,750 volts DC. at avery precise and constant level was then applied to two titaniumelectrodes located within the ion pump. Using the ion pump, a vacuum of10* to 10 Torr was created within the nickel probe. The nickel probe wasthen inserted into the liquid sodium having a temperature of 500 C.flowing through pipe 16. Hydrogen atoms in the liquid sodium thendiffused through the wall of the nickel probe and were drawn into theion pump, wherein the hydrogen atoms were ionized. The current generatedby the ionization of the hydrogen atoms was then measured, and sincethis current is linearly related to the number of hydrogen atoms ionizedin the ion pump, as previously explained, it was indicative of thehydrogen concentration in the liquid sodium. Results have shown thatthis method is sufficiently sensitive to detect a hydrogen concentrationof 0.1 ppm :t a 1 percent change. The nickel probe and ion pump wereevacuated prior to inserting the nickel probe into the liquid sodium inorder to check for any leaks in the system.

It is important that the vacuum created within the nickel probe bewithin the stated range of 10' to 10' Torr. A vacuum higher than 10'Torr will allow background noise or minor fluctuations in the voltageacross the electrodes of the ion pump to interfere with consistent andcorrect readings of the ion pump current due to the natural hydrogengases in the system, thereby creating fluctuations in the ion pumpcurrent and making the device and method insensitive and unreliable. Ifthe vacuum is lower than 10' Torr, the ion pump will overheat.

The sodium coolant of a sodium-cooled nuclear reactor will have a normalhydrogen concentration level somewhere in the range of approximately 0.1to 2.0 ppm. The normal hydrogen concentration level will not remainconstant, however, but rather it will have a slow and expected driftbetween both ends of an expected concentration range, such as between0.1 and 0.5 ppm. This must be taken into account when attempting todetect water leaks by way of hydrogen concentration changes. Therefore,in using the abovedescribed method, any unexpected increase in hydrogenconcentration at variance with the norm would indicate a water leak andthereby allow the nuclear reactor to be shut down before any significantdamage or wastage occurs.

This device and method must be sufficiently sensitive to detect waterleaks of 1.0 X 10- lb/sec, a leak rate safely below that at whichsignificant damage and metal wastage occur. This means detecting ahydrogen concentration increase of about 0.004 ppm with a sodium flowrate of l X 10 lb/hr, which is a 4 percent increase if the normalhydrogen concentration is about 0.1 ppm.

With either a slower sodium flow rate and/or a greater leak rate at anormal hydrogen concentration of 0.1 ppm, the percent increase inhydrogen concentration is much greater. Tests have indicated that theabovedescribed device and method are sensitive to a l percent increasein hydrogen concentration at a normal hydrogen concentration level of0.1 ppm.

It is also necessary in order to avoid significant damage and wastagethat water leaks be detected quickly. Hence, a leak detector mustrespond rapidly with the above-mentioned sensitivity to changes in thehydrogen concentration in liquid sodium. To avoid said damage, a leak of0.01 lb/sec should be detected within 0.5 to 5.0 minutes after the onsetof such leak. The response time of the device and method describedherein depends mainly on the rate of hydrogen diffusion through the wallof the nickel probe. Calculations indicate that for a 0.0l-inch-thicknickel probe at 500 C., 70 percent of the eventual total change inhydrogen flux would occur after only 10 seconds. Therefore, the deviceand method described herein has a sufficiently rapid response time withthe required sensitivity.

Another necessity for such a leak detector is that it be reliable. Thedevice and method described herein once in operation need no furtheradjustments or calculations. This device has the advantages of beinginexpensive, compact and permanently installed while operatingcontinuously with the required sensitivity and responsiveness. It willcontinue to do so without recalculation so long as air-tight integrityis insured and the above-discussed critical limitations are met.

While the invention relates broadly to a device for and method ofmeasuring the hydrogen concentration in liquid sodium, as has beendisclosed, the device and method can be used for the detection of waterleakage into the liquid sodium coolant of a sodium-cooled nuclearreactor based upon measuring hydrogen concentration changes in theliquid sodium coolant. The disclosed device and method have thesensitivity, rapid response, and reliability required for such a deviceand method if they are to be effective. Since there may be as many as 30to 40 water-leak-detecting units on a sodium-cooled nuclear reactor, thefact that the disclosed device and method are relatively inexpensive isanother advantage. Also, they have the further advantage of continuousmeasurement of hydrogen concentration and do not have the disadvantageof requiring removal of sodium from the system in order to make hydrogenconcentration measurements, such removal of sodium being slow andinaccurate as well as placing personnel in the position of possibleirradiation.

It will be understood that the invention is not to be limited to thedetails given herein but that it may be modified within the scope of theappended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A device for measuring hydrogen concentration in liquid sodiumcomprising a tubular, thin-wall nickel probe, which has been annealed ata temperature of 600 to 900 C. for 10 to 60 hours, having an outersurface exposed to the liquid sodium; an ion pump connected to saidtubular nickel probe operable to evacuate the interior of said nickelprobe whereby hydrogen atoms in the liquid sodium difiuse through thewall of the nickel probe and into the interior thereof and are drawninto the ion pump wherein said hydrogen atoms are ionized; means forapplying a voltage to said ion pump, said voltage being maintained at asufficiently precise and constant level so as to result in the currentin said ion pump being constant to within $0.1 percent for anyparticular concentration of hydrogen in said ion pump; and means foraccurately measuring the current in said ion pump, the current in theion pump being linearly related to the number of hydrogen atoms beingionized in the ion pump and thereby being indicative of the hydrogenconcentration in the liquid sodium.

2. The device according to claim 1 wherein said device includes meansfor initially decreasing the pressure within said ion pump and saidnickel probe to approximately l0' Torr.

3. The device according to claim 2 wherein said nickel probe has a wallthickness of 0.008 to 0.020 inch, an inner diameter no greater than 0.5inch, a length of l to 4 inches, and a surface area of 10 to 60 2.

4. The device according to claim 3 wherein said ion pump contains twotitanium or one titanium and one tantalum electrodes and has a pumpingrate of l to 20 liters/second.

5. The device according to claim 4 wherein said means for applying anaccurately controlled voltage to said ion pump comprises an ion pumpcontroller, said controller converting an A.C. input to a DC. output of2,700 to 5,000 volts DC. and applying said output voltage to theelectrodes of said ion pump, and voltageregulating means for maintainingsaid voltage at said sufficiently precise and constant level.

6. The device according to claim 3 wherein said nickel probe comprises atubular member, said tubular member being 1 inch in length and having aninner diameter of nine thirty-seconds inch and a wall thickness of 0.01inch; and hollow, circumferential nickel fins, numbering 15 fins perinch of length of said tubular member, having a wall thickness of 0.01inch and projecting three thirty-seconds inch out from the outer surfaceof said tubular member, said fins, the interiors of which are open tothe interior of said tubular member, providing increased mechanicalstrength and increased surface area for greater hydrogen diffusion, thesurface area of said nickel probe being approximately 40 cm 7. Thedevice according to claim 6 wherein said nickel probe has been annealedat 800 C. for 25 to 30 hours.

8. The device according to claim 7 wherein the ion pump contains twotitanium electrodes 0.125 inch in thickness and has a pumping rate of ll liters/second.

9. The device according to claim 8 wherein said means for applying anaccurately controlled voltage to said ion pump comprises an ion pumpcontroller, said controller converting a volt A.C. input to a DC. outputof 4,750 volts DC. and applying said output voltage to the electrodes ofsaid ion pump, and a voltage regulator wherein the voltage applied tothe electrodes of said ion pump is maintained at a sufficiently preciseand constant level so as to result in the current in said ion pump beingconstant to within i005 percent for any particular concentration ofhydrogen in said liquid sodium; and wherein said means for accuratelyindicating current in said ion pump comprises a current meter whereinthe current generated in said ion pump by the ionization of hydrogenatoms is indicated in terms of the hydrogen concentration in said liquidsodium to a sensitivity of 0.1 ppm 1 1 percent.

10. A method for measuring hydrogen concentration in liquid sodiumcomprising connecting a tubular, thinwall nickel probe to an ion pump,said nickel probe having been annealed at a temperature of 600 to 900 C.for to 60 hours; applying and maintaining a voltage to said ion pump ata sufficiently precise and constant level so as to result in the currentin said ion pump being constant to within 10. 1 percent for anyparticular concentration of hydrogen in said ion pump; creating a vacuumwith said ion pump of 10' to 10' Torr within the nickel probe;contacting the outer surface of said nickel probe with liquid sodium,thereby causing hydrogen atoms in said liquid sodium to diffuse throughthe wall of the nickel probe and into the interior thereof and be drawninto said ion pump wherein the hydrogen atoms are ionized; and measuringthe current generated by the ionization of the hydrogen atoms within theion pump, said current being linearly related to the number of hydrogenatoms ionized and thereby indicative of the hydrogen concentration inthe liquid sodium.

11. A method for detecting water leakage into the liquid sodium coolantof a liquid sodium-cooled nuclear reactor comprising connecting atubular, thinwall nickel probe to an ion pump, said nickel probe havingbeen annealed at a temperature of 600 to 900 C. for 10 to 60 hours;applying and maintaining a voltage to said ion pump at a sufficientlyprecise and constant level so as to result in the current in said ionpump being constant to within 10.1 percent for any particularconcentration of hydrogen in said ion pump; creating a vacuum with saidion pump of 10' to 10' Torr within the nickel probe; inserting saidnickel probe into the liquid sodium coolant whereby the outer surface ofsaid nickel probe is in contact with the liquid sodium, thereby causinghydrogen atoms in said liquid sodium coolant to diffuse through the wallof the nickel probe and the interior thereof and be drawn into said ionpump wherein the hydrogen atoms are ionized; and continuously measuringthe current generated by the ionization of the hydrogen atoms within theion pump, said current being linearly related to the number of hydrogenatoms ionized and therefore continuously indicating the hydrogenconcentration in the liquid sodium, any unexpected increase of saidcurrent being indicative of water leakage into said liquid sodiumcoolant.

2. The device according to claim 1 wherein said device includes meansfor initially decreasing the pressure within said ion pump and saidnickel probe to approximately 10 3 Torr.
 3. The device according toclaim 2 wherein said nickel probe has a wall thickness of 0.008 to 0.020inch, an inner diameter no greater than 0.5 inch, a length of 1 to 4inches, and a surface area of 10 to 60 cm2.
 4. The device according toclaim 3 wherein said ion pump contains two titanium or one titanium andone tantalum electrodes and has a pumping rate of 1 to 20 liters/second.5. The device according to claim 4 wherein said means for applying anaccurately controlled voltage to said ion pump comprises an ion pumpcontroller, said controller converting an A.C. input to a D.C. output of2,700 to 5,000 volts D.C. and applying said output voltage to theelectrodes of said ion pump, and voltage-regulating means formaintaining said voltage at said sufficiently precise and constantlevel.
 6. The device according to claim 3 wherein said nickel probecomprises a tubular member, said tubular member being 1 inch in lengthand having an inner diameter of nine thirty-seconds inch and a wallthickness of 0.01 inch; and hollow, circumferential nickel fins,numbering 15 fins per inch of length of said tubular member, having awall thickness of 0.01 inch and projecting three thirty-seconds inch outfrom the outer surface of said tubular member, said fins, the interiorsof which are open to the interior of said tubular member, providingincreased mechanical strength and increased surface area for greaterhydrogen diffusion, the surface area of said nickel probe beingapproximately 40 cm2.
 7. The device according to claim 6 wherein saidnickel probe has been annealed at 800* C. for 25 to 30 hours.
 8. Thedevice according to claim 7 wherein the ion pump contains two titaniumelectrodes 0.125 inch in thickness and has a pumping rate of 11liters/second.
 9. The device according to claim 8 wherein said means forapplying an accurately controlled voltage to said ion pump comprises anion pump controller, said controller converting a 110 volt A.C. input toa D.C. output of 4,750 volts D.C. and applying said output voltage tothe electrodes of said ion pump, and a voltage regulator wherein thevoltage applied to the electrodes of said ion Pump is maintained at asufficiently precise and constant level so as to result in the currentin said ion pump being constant to within + or - 0.05 percent for anyparticular concentration of hydrogen in said liquid sodium; and whereinsaid means for accurately indicating current in said ion pump comprisesa current meter wherein the current generated in said ion pump by theionization of hydrogen atoms is indicated in terms of the hydrogenconcentration in said liquid sodium to a sensitivity of 0.1 ppm + or - 1percent.
 10. A method for measuring hydrogen concentration in liquidsodium comprising connecting a tubular, thin-wall nickel probe to an ionpump, said nickel probe having been annealed at a temperature of 600* to900* C. for 10 to 60 hours; applying and maintaining a voltage to saidion pump at a sufficiently precise and constant level so as to result inthe current in said ion pump being constant to within + or - 0.1 percentfor any particular concentration of hydrogen in said ion pump; creatinga vacuum with said ion pump of 10 6 to 10 8 Torr within the nickelprobe; contacting the outer surface of said nickel probe with liquidsodium, thereby causing hydrogen atoms in said liquid sodium to diffusethrough the wall of the nickel probe and into the interior thereof andbe drawn into said ion pump wherein the hydrogen atoms are ionized; andmeasuring the current generated by the ionization of the hydrogen atomswithin the ion pump, said current being linearly related to the numberof hydrogen atoms ionized and thereby indicative of the hydrogenconcentration in the liquid sodium.
 11. A method for detecting waterleakage into the liquid sodium coolant of a liquid sodium-cooled nuclearreactor comprising connecting a tubular, thin-wall nickel probe to anion pump, said nickel probe having been annealed at a temperature of600* to 900* C. for 10 to 60 hours; applying and maintaining a voltageto said ion pump at a sufficiently precise and constant level so as toresult in the current in said ion pump being constant to within + or -0.1 percent for any particular concentration of hydrogen in said ionpump; creating a vacuum with said ion pump of 10 6 to 10 8 Torr withinthe nickel probe; inserting said nickel probe into the liquid sodiumcoolant whereby the outer surface of said nickel probe is in contactwith the liquid sodium, thereby causing hydrogen atoms in said liquidsodium coolant to diffuse through the wall of the nickel probe and theinterior thereof and be drawn into said ion pump wherein the hydrogenatoms are ionized; and continuously measuring the current generated bythe ionization of the hydrogen atoms within the ion pump, said currentbeing linearly related to the number of hydrogen atoms ionized andtherefore continuously indicating the hydrogen concentration in theliquid sodium, any unexpected increase of said current being indicativeof water leakage into said liquid sodium coolant.